The ability of human beings to maintain stability and balance is controlled by the vestibular system. This system provides the central nervous system with the information needed to maintain balance and stability.
In FIG. 1, the vestibular system includes three mutually-orthogonal ring-shaped tubes, referred to as the semicircular canals 102a-c, that are filled with endolymph fluid. The semicircular canals are formed by a membrane called the membranous labyrinth. Each of the semicircular canals 102a-c is disposed inside a hollow bony tube (not shown in the diagram), called the bony labyrinth, that extends along the contours of the semicircular canals. Lining the interior walls of the bony labyrinth is a thin membrane called the endosteum. The bony labyrinth is filled with a fluid called the perilymph.
As further shown in FIG. 1, each semicircular canal 102a-c terminates in an enlarged balloon-shaped section called the ampulla (marked 104a-c in FIG. 1). Inside each ampulla is the cupula 106a-c, on which hair cells are embedded.
Generally, as the semicircular canals 102a-c rotate due to rotational motion of a head, the endolymph fluid inside the canal will lag behind the moving canals, and thus cause the hair cells on the cupula to bend and deform. This deformation stimulates nerves attached to the hair cells, resulting in the generation of nerve signals that are sent to the central nervous system. These signals are decoded to provide the central nervous system with motion information.
The three canals together provide information about rotation in all three spatial dimensions. The other endorgans in the vestibular system are the otolith organs, the utricle and the saccule. These endorgans act as linear accelerometers and respond to both linear motion and gravity.
In response to the vestibular nerve impulses, the central nervous system perceives motion and, in response, controls the movement of various muscles in an effort to maintain balance.
Dehiscence is a medical condition in which the bony labyrinth surrounding one or more of the semicircular canals is so thin that small changes of air pressure in the ear (for example, resulting from sound waves), can cause the actuation of the endosteum that stimulates the vestibular system.
Another condition affecting the vestibular system is intractable benign paroxysmal positional vertigo. In this medical condition, small stones or debris formed in the semicircular canals are randomly displaced inside the endolymph fluid. This disturbs the endolymph fluid, which in turn deflects the hair cells on the cupula. Thus, the patient perceives motion that is inconsistent with his actual motion.
Person suffering from dehiscence, intractable benign paroxysmal positional vertigo, or other conditions resulting in an overly sensitive vestibular system, experience vertiginous symptoms such as dizziness and disorientation.
Occasionally, symptoms associated with dehiscence or intractable benign paroxysmal positional vertigo subside either by themselves, or with the aid of non-invasive treatment (e.g., simple head exercises to remove the debris from the endolymph fluid in situations involving intractable benign paroxysmal positional vertigo). However, in some situations it becomes necessary to perform a surgical procedure called “canal plugging” to alleviate such conditions. The goal of canal plugging is to block most of the canal's function without significantly affecting other semicircular canals or parts of the ear. This procedure, however, poses a small risk to hearing. More troubling, however, is that canal plugging is irreversible. Thus, although canal plugging permanently relieves vertiginous symptoms, it does so at the cost of making it non-feasible for patients to benefit from newly-discovered treatment options.